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Area forecast discussion 
National Weather Service Blacksburg Virginia
525 am EDT Thu Jul 28 2016

Synopsis...

Low pressure will move along a stalled front from the mid
Mississippi Valley to the Ohio Valley today and tonight. This wavy
frontal system will remain across the region through Monday. The
front is expected to drift south and dissipate next Tuesday and
Wednesday.

&&

Near term /through tonight/...
as of 430 am EDT Thursday

Cluster of showers and thunderstorms was tracking northeast through
western part of the County Warning Area at 400am. High resolution
guidance has a majority of this precipitation north of the forecast
area at 13z/9am. There will be some residual cloud cover this
morning which will cut back on the potential heating and
instability. Temperatures will still climb into the 80s today in the
mountains and into the 90s in the Piedmont. Starting with muggy
conditions this morning in part due to surface dew points in the
upper 60s to lower 70s. Heat index will top out around 100 in the
east of the Blue Ridge this afternoon but will fall short of advisory
level values.

Short waves over the mid Mississippi Valley early this morning are
forecast to track into the Ohio Valley by Friday morning. This will
provide better synoptic scale lift plus forecast area will be in the
right entrance region of the upper jet this afternoon and evening.
Low and mid level winds increase from the southwest to west by late
this afternoon which will increase the helicity. BUFKIT forecast
soundings were showing some decent speed shear. Directional shear
becomes stronger this afternoon too as the surface low that was over
southeast Missouri this morning moves east and backs the surface
winds to the southeast.

Once the short wave moves east...surface through mid level winds
turn to the northwest and best lift will be confined to the western
County Warning Area. No change in air mass overnight so minimum
temperatures will be similar to past few mornings.

&&

Short term /Friday through Sunday night/...
as of 330 am EDT Thursday...

A shallow slow moving upper trof will remain across the eastern part of
the country through the weekend. This will keep a steady stream of
short waves moving through the region, along with deep moisture and a
lingering frontal boundary just off to our southeast. This pattern will
produce broad synoptic lift and enhance convective activity that
develops in the unstable environment, and give US increasing chances
for showers and thunderstorms each day through the weekend with the
best chances mainly along and west of the Blue Ridge. Shear will be
limited so any marginal severe threat will be with pulse
storms/clusters, and the concern for Hydro issues will be growing as
successive rounds of locally heavy rain will start to add up.

Temperatures will be right around normal for late July with highs
generally around 90 east of the ridge, low/mid 80s west.

&&

Long term /Monday through Wednesday/...
as of 330 PM EDT Wednesday...

The generalized pattern over the Continental U.S. Will be slow to change in the
extended period as upper ridge builds over the western states an
broad troughing takes hold across the eastern U.S. Expect several
shortwaves will crest the western ridge and help to amplify the
eastern trough early in the period. Meanwhile a surface frontal
boundary will persist in the vicinity of the mid-Atlantic through
the period oscillating somewhat north and south in response to short-
wave activity and modified by rounds of mainly afternoon/evening convection.
The air mass will remain warm and humid through the period with
daily highs near to slightly above normal and lows above normal
due to the high humidity and considerable cloudiness at times. By
Wednesday indications are that 500 mb heights will begin to rise again
with somewhat drier and hotter conditions for mid-week period.

&&

Aviation /09z Thursday through Monday/...
as of 200 am EDT Thursday...

Area of showers and thunderstorms with MVFR ceilings and
visibilities over eastern Kentucky and southwest Virginia will
continue to move northeast this morning. Along the Blue Ridge and
into the Piedmont of Virginia and North Carolina areas of fog and
stratus will develop. Observations showed high surface dew points
with little to no dew point depression. High confidence of IFR to
LIFR fog at kbcb and klwb this morning. Medium confidence how far
visibilities will drop at kblf and kroa. The fog will dissipate
after sunrise with VFR visibility by 14z/10am. May take longer for
ceilings to lift back to VFR.

Storms will develop over the mountains during the early afternoon
and then move east into the foothills and Piedmont during the mid-
late afternoon. There is a high likelihood for thunderstorms in the vicinity for all of
the flight terminals in the central Appalachians this afternoon
but timing of MVFR conditions too uncertain to include in the body of
the tafs at this time. BUFKIT showed a favorable shear profile for
more organized storms and the potential for microburst winds
within the thunderstorm cores leading to isolated surface gusts of
30-50kts.

Coverage of thunderstorms will diminish after sunset in the
Piedmont. Scattered showers will continue in the mountains
overnight. Models suggested ceilings will lower to MVFR with deep
westerly winds around 06z. Have not lowered the ceilings in the
tafs at this point.

Extended aviation discussion...

An upper ridge of high pressure will remain just south of the
area and a residual frontal boundary will remain over the area through
Monday. This will allow for periodic, mainly diurnally
driven, deep convection. A more widespread sub-VFR potential
exists into Friday per a strong wave of low pressure which will
ripple east along a stalled front. After the passage of this
wave, some decrease in coverage of precipiation is expected over
the weekend. In addition to the thunderstorm threat, late night
and early morning fog will likely occur at the usual valley
locations.

&&

Climate...
record warm minimum temperatures for July 28

Bluefield WV.....69 in 2010
Danville Virginia......76 in 1997
Lynchburg Virginia.....77 in 1930
Roanoke Virginia.......80 in 1930
Blacksburg Virginia....68 in 1987

&&

Rnk watches/warnings/advisories...
Virginia...none.
NC...none.
WV...none.

&&

$$
Synopsis...air mass
near term...ams/wp
short term...mbs
long term...mbs/pc
aviation...ams/PM
climate...air mass

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